1. Field of the Invention
The present invention relates to a document feeding device that feeds documents and that can be used with image forming apparatuses such as copying machines, printers, facsimiles, and scanners. The present invention also relates to an image forming apparatuses having the document feeding device.
2. Description of the Related Art
Some image forming apparatuses are provided with a document feeding device that automatically feeds a plurality of documents, one at a time to a document reading section. A typical document feeding device is mounted at the top of the image forming apparatus.
The document feeding device separates documents that are stacked on a document tray one at a time from the uppermost one, and feeds the separated document to a document reading section. An image on a surface of the document is read by the document reading section and the document is then ejected onto a document output tray provided on the most downstream side of a document feeding path. These operations need to be performed in a limited amount of space.
To achieve size reduction of the document feeding device, a document conveying path extending from the document tray to the document output tray, via the document reading section, often has a curved shape. The document conveying path also includes a conveying guide member for forming a document feeding space, and conveying rollers for nipping and feeding the document.
When a document passes through the curved document conveying path, it also curves along the document conveying path against its elasticity. Hence, when an upstream end of the document in the feeding direction (the rear end in the feeding direction) is released from the nip between the conveying rollers or passes through a portion where a surface of the conveying guide member is at a retracted position, it can collide with the surface of the conveying guide member due to its elasticity. The impact of the end of the document with the conveying guide member can cause much noise when the elasticity of the document is great.
Devices for preventing the impact of the upstream end of a document and the conveying guide member during feeding have been proposed heretofore. For example, in a sheet feeding mechanism, a buffer plate comprised of sponge or rubber is provided between two conveying guide members arranged in the feeding direction.
In this sheet conveying mechanism, even when, due to its elasticity, the upstream end, in the feeding direction, of a sheet passing between the two conveying guide members collides with the conveying guide members the impact of the collision is absorbed by the buffer plate, so that the noise is reduced.
Elasticity of the document (sheet) varies according to the type, material, and size of the document, and how the document bends. Even when the type, material, and size of the document are not different, the characteristics of the document, such as elasticity and coefficient of friction, can vary greatly according to changes in the ambient environment, for example, in temperature or humidity. In this situation, it is difficult to estimate which portion of the document conveying surface of the conveying guide member the upstream end of the document will collide with and what noise will be caused by the impact.
Accordingly, in the above-described sheet conveying mechanism, it is necessary to use the buffer plate across a wide area. This requirement tends to greatly increase the development period and cost. Hence, it is desired that the document not collide with the document conveying surface of the conveying guide member.